1. Field of the Invention
The present invention relates to an active-matrix display apparatus having display elements each included in one of pixel circuits arranged on a display area to form a matrix, a driving method to be adopted by the display apparatus and electronic equipment employing the display apparatus. In the following description, each of the display elements is also referred to as an electro-optical device.
2. Description of the Related Art
An example of the display apparatus is a liquid-crystal display apparatus employing liquid-crystal cells as display elements, each of which is referred to as an electro-optical device. The liquid-crystal display apparatus is characterized in that the display apparatus has a small thickness and a low power consumption. Various kinds of electronic equipment make use of such a liquid-crystal display apparatus, taking advantage of its characteristics. The electronic equipment includes a PDA (Personal Digital Assistant), a cell phone, a digital camera, a video camera and the display unit of a personal computer.
FIG. 1 is a block diagram showing a typical configuration of the liquid-crystal display apparatus 1 (see Japanese Patent laid-open No. Hei 11-119746 and Japanese Patent laid-open No. 2000-298459). As shown in FIG. 1, the liquid-crystal display apparatus 1 employs an effective pixel section 2, a vertical driving circuit (VDRV) 3 and a horizontal driving circuit (HDRV) 4.
In the effective pixel section 2, a plurality of pixel circuits 21 are arranged to form a matrix. Each of the pixel circuits 21 includes a thin-film transistor TFT21 functioning as a switching device, a liquid-crystal cell LC21 and a storage capacitor Cs21. The first pixel electrode of the liquid-crystal cell LC21 is connected to the drain electrode (or the source electrode) of the thin-film transistor TFT21. The drain electrode (or the source electrode) of the thin-film transistor TFT21 is also connected to one the first electrode of the storage capacitor Cs21.
Scan lines (or gate lines) 5-1 to 5-m are each provided for a row of the matrix and connected to the gate electrodes of the thin-film transistors TFT21 employed in the pixel circuits 21 provided on the row. The scan lines 5-1 to 5-m are arranged in the column direction. Signal lines 6-1 to 6-n arranged in the row direction are each provided for a column of the matrix.
As described above, the gate electrodes of the thin-film transistors TFT21 employed in the pixel circuits 21 provided on a row are connected to a scan line (one of the scan lines 5-1 to 5-m) provided for the row. On the other hand, the source (or drain) electrodes of the thin-film transistors TFT21 employed in the pixel circuits 21 provided on a column are connected to a signal line (one of the signal lines 6-1 to 6-n) provided for the column.
In addition, in the case of an ordinary liquid-crystal display apparatus, a capacitor line Cs is provided separately. The storage capacitor Cs21 is connected between the capacitor line Cs and the first electrode of the liquid-crystal cell LC21. Pulses having the same phase as a common voltage Vcom are applied to the capacitor line Cs. In addition, the storage capacitor Cs21 of every pixel circuit 21 on the effective pixel section 2 is connected to the capacitor line Cs serving as a line common to all the storage capacitors Cs21.
On the other hand, the second pixel electrode of the liquid-crystal cell LC21 of every pixel circuit 21 is connected to a supply line 7 serving as a line common to all the liquid-crystal cells LC21. The supply line 7 provides the common voltage Vcom, which is a series of pulses with a polarity typically changing once every horizontal scan period. One horizontal scan period is referred to as 1H.
Each of the scan lines 5-1 to 5-m is driven by the vertical driving circuit 3 whereas each of the signal lines 6-1 to 6-n is driven by the horizontal driving circuit 4.
The vertical driving circuit 3 scans the rows of the matrix in the vertical direction or the row-arrangement direction in one field period. In the scan operation, the vertical driving circuit 3 scans the rows sequentially in order to select a row at one time, that is, in order to select pixel circuits 21 provided on a selected row as pixel circuits connected to a gate line (one of the gate lines 5-1 to 5-m) provided for the selected row. To put it in detail, the vertical driving circuit 3 asserts a scan pulse GP1 on the gate line 5-1 in order to select pixel circuits 21 provided on the first row. Then, the vertical driving circuit 3 asserts a scan pulse GP2 on the gate line 5-2 in order to select pixel circuits 21 provided on the second row. Thereafter, the vertical driving circuit 3 sequentially asserts gate pulses GP3 . . . and GPm on the gate lines 5-3 . . . and 5-m respectively in the same way.
FIGS. 2A to 2E show timing charts of signals generated in execution of the so-called 1H Vcom inversion driving method of the ordinary liquid-crystal display apparatus shown in FIG. 1. To be more specific, FIG. 2A shows the timing chart of the gate pulse GP_N, FIG. 2B shows the timing chart of the common voltage Vcom, FIG. 2C shows the timing chart of the capacitor signal CS_N, FIG. 2D shows the timing chart of the video signal Vsig and FIG. 2E shows the timing chart of the signal Pix_N applied to the liquid-crystal cell.
In addition, a capacitive coupling driving method is known as another driving method. In accordance with the capacitive coupling driving method, a voltage applied to the liquid-crystal cell is modulated by making use of a capacitive coupling effect from a capacitor line Cs (see Japanese patent laid-open No. Hei 2-157815).